Method of piling



April 2, 1968 s. SEROTA METHOD OF FILING Filed Nov. 25, 1966 FEG.2.

FIG.3.

INVENTOR ATTORNEYS United States Patent 3,375,670 METHOD OF PILING Stanley Serota, 111 Westminster Bridge Road, London, SE. 1, England Filed Nov. 25, 1966, Ser. No. 597,083 Claims priority, application Great Britain, Nov. 26, 1965, 50,320/65 3 Claims. (Cl. 6153.6)

This invention relates to a method of securing a pile in the ground and is of particular utility in providing a load-bearing pile or an anchorage against tensile forces, such as might be required for electrical transmission lines.

In those cases where a tubular casing, normally filled with concrete, remains in the ground the load-bearing capacity of the pile against either compressive or tensile forces depends largely upon the coeflicient of friction between the outside of the pile and the surrounding ground. If the pile is of metal, as is usual, this coefficient of friction may not be very great and in many cases reliance must be placed upon the end bearing ability of the pile. To provide a greater load bearing capacity, the crosssectional area of the pile must be increased, with a corresponding increase in the cost of the casing and of installation.

It is an object of the present invention to provide a method of piling which provides a more secure anchorage against both compressive and tensile forces by virtue of a more secure engagement between the outer walls of the pile and the surrounding ground.

According to the invention there is provided a method of securing a pile casing in the ground comprising inserting into the ground a substantially tubular casing of which the wall is at least in part corrugated in a longitudinal direction, inserting an expanding mechanism into said casing at a level below ground level, operating said mechanism so that those parts of said wall lying furtherest inwards are deformed outwardly so as substantially to remove said corrugations and to render said walls substantially straight longitudinally, and removing said mechanism from the casing.

According to a further aspect of the invention the expansion process may also increase the overall dimensions of the pile and may also leave vestiges of the original corrugations; and the pile may subsequently or at the same time be further expanded to form a new pattern of corrugations of deformations.

In order that the invention shall be clearly understood, embodiments thereof will now be described, by Way of example only, with reference to the accompanying drawings in which:

FIGURES 1 and 2 show sectional view of a pile casing in position in the ground before and after deformation, in the performance of a first embodiment of the invention; and

FIGURES 3 and 4 show views similar to FIGURES l and 2 for a second embodiment.

Considering first FIGURES l and 2, there is shown a light metallic tubular casing 10, which may suitably be of gauge thickness between 8 and 16, which has been inserted in a soft soil 11 by any convenient means. These means may involve drilling a hole using a drill casing, inserting the light casing within the drill casing, withdrawing the drill casing and allowing the soil to collapse around the light casing. Alternatively, the light casing may be sunk, only by driving, using a mandrel to support it as it is driven. This light casing is formed spirally by its manufacturing process, which involves wrapping a suitably curved strip around a mandrel and welding the abutting edges of the strip to form the longitudinally corrugated casing shown. Such a light casing is easy and cheap ICC to manufacture and can therefore be left within the hole permanently. In order to secure the casing in the ground, it is subjected to an expansion process by means of which the longitudinal corrugations are substantially flattened out. The innermost portions of the wall 12 are pushed outwardly by any convenient means such as hydraulic rams (not shown) at the points indicated by arrow 20, so that at the end of the operation, the section through the casing will look generally as in FIGURE 2. The overall diameter D may remain substantially the same or may increase. It is unlikely that the corrugations would be entirely eliminated, but the important effect achieved by this process lies in that in the total volume within the casing is increased, and thus continuous radial pressure is exerted against the surrounding soil by the casing after the operation.

The continuous radial pressure thereby achieved provides an extremely secure anchorage against longitudinal movement of the casing, which may afterwards be filled in with concrete to finish the pile.

Although this degree of radial expansion of the casing will normally be suflicient to prOVide the necessary anchorage, it is of course possible to further locally expand the material of the casing until, for example, it .again takes up a corrugated configuration the new corrugations of which need not necessarily correspond with the old.

The expansion is performed by means of an expanding mechanism, for example a simple cylindrical expander which is hydraulically operated. The mechanism is lowered into the hollow casing once the drill casing has been removed, expanded to cause flattening of the corrguations, and then withdrawn again before filling-in with concrete. If further expansion or re-corrugation of the walls is required, provision may be made for doing this with the same mechanism, or with a separate one.

FIGURES 3 and 4 show a further embodiment of a method according to the invention in which the light casing is inserted into a pre-drilled, self-supporting hole in firm ground. In this case, the surrounding soil does not collapse around the tube. The casing is inserted after withdrawal of the drill casing, rather than before withdrawal.

In this instance, it will normally be advisable to produce some further outward expansion of the tube beyond that produced simply by flattening out the corrugations in the casing, although the latter does usually result in an increased overall diameter. This may be achieved by recorrugation as described above, and the form of a tube which has been subjected to this method is shown in FIGURE 4. The innermost portions of the corrugations 13 are shown as having been deformed outwardly, firstly until the casing is substantially cylindrical and straight longitudinally, and then further until these portions 13 become the outermost portions. The re-corrugations will normally be annular rather than helical as the original corrugations were.

The light casing inserted initially will, as explained above, normally have corrugations which extend over the full length of the casing, but which need not necessarily do so. Equally, the proportion of the length which is acted upon by the expanding mechanism may be less than the total length of the tube, or less than the total portion of the tube which is corrugated.

The initial shape of the casing is not restricted to the helical by corrugated form, and may alternatively be annularly corrugated, fluted, or deformed in any convenient manner to provided local irregularity in the wall of the casing. The amount by which the walls are deformed once the casing is inserted in the hole depends upon the grip which it is required to obtain in the soil. It will normally, however, be necessary to expand the existing deformations in the wall at least sufficiently to render its contour generally longitudinally fiat or straight, and extra grip may then be obtained by further expansion, e.g., by rte-corrugation.

It should not be thought that this method of securing a pile is dependent upon the mechanical grip achieved between any projections on the casing and the surrounding soil. The major effect is achieved through the increased external friction due to the residual radial pressure achieved by outward deformation of the casing. This can be demonstrated by the fact that the grip achieved with a casing in which external projections on the casing key with a clay soil, for example can be upwards of 2 /2 times the shear strength of the soil.

I claim:

1. A method of securing a tubular pile casing in the ground comprising inserting into the ground a substantially tubular casing of which the wall is at least partially corrugated in a longitudinal direction, inserting an expanding mechanism into said casing at a level below ground level, operating said mechanism so that those parts of said wall lying furthest inwards are deformed outwardly so as to substantially remove said corrugations and to render said walls substantially straight longitudinally, and removing said mechanism from the casing.-

2. A method as claimed in claim 1, wherein the wall of said casing is further deformed by said mechanism so that the overall diameter of the casing is increased.

3. A method as claimed in claim 2, wherein the overall diameter of said casing is increased by the formation of further corrugations in the wall of the casing after the original corrugations havebeen substantially removed by said mechanism.

References Cited UNITED STATES PATENTS 2,977,770 4/1961 Hoppe 61--53.72 3,197,967 8/1965 Col-field 61-5168 FOREIGN PATENTS 599,786 7/1934 Germany.

JACOB SHAPIRO, Primary Examiner. 

1. A METHOD OF SECURING A TUBULAR PILE CASING IN THE GROUND COMPRISING INSERTING INTO THE GROUND A SUBSTANTIALLY TUBULAR CASING OF WHICH THE WALL IS AT LEAST PARTIALLY CORRUGATED IN A LONGITUDINAL DIRECTION, INSERTING AN EXPANDING MECHANISM INTO SAID CASING AT A LEVEL BELOW GROUND LEVEL, OPERATING SAID MECHANISM SO THAT THOSE PARTS OF SAID WALL LYING FURTHEST INWARDS ARE DEFORMED OUTWARDLY SO AS TO SUBSTANTIALLY REMOVE SAID CORRUGATIONS AND TO RENDER SAID WALLS SUBSTANTIALLY STRAIGHT LONGITUDINALLY, AND REMOVING SAID MECHANISM FROM THE CASING. 